The carrier dynamical issues for extending the operating wavelength of quantum cascade lasers into the Terahertz regime

The potential operating performance of Terahertz quantum cascade lasers are compared with contemporary shorter wavelength mid-infrared devices from the viewpoint of the carrier dynamics within the active region. It has been shown that the internal quantum efficiency for radiative transitions between two subbands in GaAs at Terahertz frequencies is greater at low temperatures than that at mid-infrared wavelengths. It is comparable at 77 K and less at room temperature. Furthermore the internal quantum efficiency is higher for vertical intrawell transitions than diagonal interwell transitions at Terahertz frequencies